The present invention relates to devices used in percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) procedures, particularly when adapted for the dilatation of intravascular tissue and the localized delivery of a therapeutic agent to the dilatated tissue.
PTA and PTCA procedures have gained widespread acceptance in the treatment of vascular constrictions and blockages, and are increasingly favored because they involve less trauma and lower cost compared to traditional alternative procedures such as coronary bypass. However, the recurrence of total or partial blockage, usually from three to six months after the procedure, continues to be of concern. This phenomenon, known as restenosis, appears in about thirty percent or more of the cases that originally appear successful. Restenosis can present a risk to the patient and typically necessitates another tissue dilatation, or an alternative procedure.
Certain therapeutic agents can be administered to reduce restenosis, e.g. anti-thrombolitic agents such as heparin to prevent clotting, and anti-proliferative agents such as dexamethasone to prevent smooth muscle cell migration and proliferation. Catheters have been developed for local delivery of therapeutic agents. For example, U.S. Pat. No. 5,087,244 (Wolinsky) discloses a catheter with a substantially inelastic distal balloon with a plurality of minute (e.g. 25 micrometer) perforations said to provide a low, weeping flow rate of a liquid to the surrounding tissue. Another approach to localized delivery involves inflating spaced apart proximal and distal balloons against arterial walls to provide a chamber about a treatment site, then delivering an agent into the chamber, e.g. as disclosed in U.S. Pat. No. 4,824,436 (Wolinsky).
Several devices have been developed to perform both the dilatation and drug delivery functions. Examples include U.S. Pat. No. 5,415,636 (Forman), assigned to the assignee of this application, featuring a catheter with a dilatation balloon and a pair of occlusion balloons, one proximal and one distal with respect to a drug delivery port. U.S. Pat. No. 4,994,033 (Schockey), also assigned to the present assignee, discloses an intravascular dilation and delivery catheter with inner and outer hollow expansible sleeves at the distal ends of three concentric catheters. The outer sleeve includes minute openings through which a liquid dispersant perfuses as the inner sleeve is expanded.
U.S. Pat. No. 5,049,132 (Shaffer) discloses a two-balloon catheter in which the outer balloon includes apertures sized to permit flow of a liquid through the balloon to treat tissue, and in which the outer balloon is spot-sealed to an inner balloon in several areas spaced from the ends of the balloons. In U.S. Pat. No. 5,421,826 (Crocker) a drug delivery balloon with perforations is disposed concentrically about a dilatation balloon, with the two balloons preferably heat sealed together at the proximal and distal ends. The dilatation balloon is used to expel the drug out of the drug delivery balloon, and pulls the delivery balloon with it when aspirated, to minimize external dimensions.
The aforementioned approaches have proven useful in certain circumstances. However, the growing interest in gene therapy for treating cardiovascular diseases including restenosis, and the nature of coronary arteries, raise challenges not yet adequately addressed.
More particularly, gene therapy involves large, complex molecules that tend to rapidly combine with proteins in the bloodstream to lose their efficacy. This raises a need to protect gene therapy agents from contact with the blood as they are maintained in contact with a vessel wall under treatment. Similarly, a freshly cracked lesion can be more effectively medicated if it is protected from contact with blood during treatment.
Coronary vasculature includes many collateral arteries and branches in which the conventional two-balloon approach does not effectively block or divert the flow of blood, nor do the conventional non-distensible dilatation and drug delivery balloons establish a conforming contact with the arterial wall at low pressures.
Therefore, it is an object of the present invention to provide a drug delivery device for effectively maintaining a therapeutic agent in contact with vessel walls while protecting the vessel walls and the agent from contact with blood.
Another object is to provide a combination tissue dilatation and drug delivery device that facilitates substantially immediate treatment of a freshly cracked lesion while protecting the lesion from contact with blood.
A further object is to provide a process for treating vascular tissue including expanding a liquid permeable sheath elastically into intimate and substantially conforming contact with the vascular tissue, and causing a therapeutic agent to pass through the sheath to the surrounding tissue while the sheath remains expanded.
Yet another object is to provide a dilatation and drug delivery device in which a therapeutic agent is administered after tissue dilatation and at a pressure and flow rate determined independently of the tissue dilatation means.